Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$52.35	4.724%	$54.823	$54.82	$54.80	$54.80
Purchase #2	$36.37	10.763%	$40.2845	$40.28	$40.30	$40.30
Purchase #3	$86.89	12.351%	$97.6218	$97.62	$97.60	$97.60
Purchase #4	$50.64	5.248%	$53.2976	$53.30	$53.30	$53.30
Purchase #5	$64.86	5.718%	$68.5687	$68.57	$68.55	$68.60
Purchase #6	$37.54	13.704%	$42.6845	$42.68	$42.70	$42.70
Purchase #7	$63.86	12.123%	$71.6017	$71.60	$71.60	$71.60
7 purchase totals =	$392.51		$428.8818	$428.87	$428.85	$428.90